1. Field of the Invention
The present invention generally relates to microwave or millimeter-wave communication devices, and more particularly to a resonator, a filter, a duplexer, and a communication device for use in transmission and reception of radio waves or electromagnetic waves.
2. Description of the Related Art
Typically, resonators used in the microwave or millimeter-wave band incorporate a coaxial resonator including a dielectric block having a through-hole formed therein, an inner conductor formed within the through-hole, and an outer conductor formed on an outer surface of the dielectric block.
Compact dielectric coaxial resonators of this type have been proposed in Japanese Utility Model Application Publication No. 4-29207 and Japanese Unexamined Patent Application Publication No. 7-122914. The proposed dielectric coaxial resonators are of the type in which the inner conductor is spiral-shaped so that the axial length of the through-hole is reduced.
A typical coaxial resonator having a spiral inner conductor is a resonator formed either by a half-wave or quarter-wave line made from a single spiral micro-strip line. In such a typical coaxial resonator, therefore, a region in which the electric energy is concentrated and accumulated and a region in which the magnetic energy is concentrated and accumulated are separately and unevenly distributed. More specifically, the electric energy is accumulated in the vicinity of an open end of the line while the magnetic energy is accumulated in the vicinity of a short-circuit end of the line.
The resonator having a resonant line formed by a single micro-strip line encounters problems, in that the micro-strip line suffers from degradation of its characteristics due to the edge effect which inherently affects micro-strip lines. That is, the electric current is concentrated at the edges of the line as viewed at the cross-section of the line, that is, both ends in its width direction, and the upper and lower ends in its thickness direction. Even if the thickness of the line is increased in order to suppress power loss due to such current concentration, the edge regions in which the current concentration occurs will not be increased in size. Thus, a problem which is essentially associated with power loss due to the edge effect occurs. Accordingly, while the use of a spiral inner conductor makes it possible to reduce the axial length of the through-hole to, for example, approximately 15% of the length in the above-mentioned Japanese applications, the unloaded Q-factor is strongly deteriorated to a value of 55, as compared to a typical unloaded Q-factor of 470.
Responding to these problems, the present invention provides a resonator, a filter, a duplexer, and a communication device which have low loss characteristics and are compact, and in which power loss due to the edge effect is effectively suppressed.
To this end, in one aspect of the present invention, a resonator includes a hollow dielectric element having a hole therein, a helical line unit including a plurality of helical lines formed in the hole, and a ground electrode formed on an outer surface of the dielectric element.
With this structure, each helical line is adjacent to another helical line. Microscopically, the edge effect in the helical lines is physically significant, and the helical lines slightly suffer from the edge effect. Macroscopically, however, as these helical lines are considered together as a single helical line unit, each helical line neighbors another helical line, so that the edges of the helical lines in their width direction are essentially continuous. That is, the edge effect becomes negligible. Therefore, the current concentration at the edges of each line due to the edge effect is moderated extremely efficiently, to significantly suppress power loss.
In another aspect of the present invention, a resonator includes a cylindrical base comprising an insulator, a magnetic element or a dielectric element, and a helical line unit including a plurality of helical lines arranged on a lateral face of the cylindrical base, and these are installed in a cavity to form the resonator. Structurally, the helical line unit is identified as a central conductor of a coaxial resonator.
In another aspect of the present invention, a resonator may include a conductive shielding member. The conductive shielding member is used to confine the electromagnetic energy within a certain region, preventing unwanted emission or unwanted coupling to the outside.
In the above resonators, the helical lines are preferably interconnected by a line at a substantially equi-phase region. This provides a uniform potential at the interconnected region of the helical lines, so that the resonator including the helical lines resonates in a desired resonant mode in a stable manner, suppressing spurious responses. Since the helical lines are interconnected by a line to form a single helical line unit, a large capacitance is readily generated between a coupling electrode and the helical line unit, thereby providing strong coupling to an external circuit.
In another aspect of the present invention, a filter includes a hollow dielectric element having a plurality of holes therein and a plurality of resonators having different axes and being arranged substantially in parallel to each other. The resonators include a plurality of helical line units each including a plurality of helical lines formed in each of the holes, and a ground electrode formed on an outer face of the dielectric element. The filter further includes input/output units coupled to predetermined resonators of the plurality of resonators. Accordingly, the filter has multiple resonators coupled to each other.
In another aspect of the present invention, a filter includes a conductive cavity, and a plurality of resonators arranged in the conductive cavity so as to have different axes substantially in parallel to each other. The resonators include a plurality of helical line units each formed on a lateral face of a cylindrical base, each helical line unit including a plurality of helical lines. The filter further includes input/output units coupled to predetermined resonators of the multiple resonators. Accordingly, the filter has multiple resonators coupled to each other.
In another aspect of the present invention, a filter includes a cylindrical dielectric element having a hole therein and a plurality of resonators. The resonators include a plurality of helical line units coaxially formed in the hole, each helical line unit including a plurality of helical lines and a ground electrode formed on an outer face of the dielectric element. The filter further includes input/output units coupled to predetermined resonators of the plurality of resonators. Accordingly, the filter has multiple resonators coupled to each other.
In another aspect of the present invention, a filter includes a conductive cavity, and a plurality of resonators coaxially arranged in the conductive cavity. The resonators include a plurality of helical line units each formed on a lateral face of a cylindrical base, each including a plurality of helical lines. The helical line units are formed on a lateral face of cylindrical base. The filter further includes input/output units coupled to predetermined resonators of the multiple resonators. Accordingly, the filter has multiple resonators coupled to each other.
In another aspect of the present invention, a duplexer uses one of the previously-described filters. In other words, any of the previous fillers may be used in the duplexer, for example as a transmitter filter and a receiver filter in a shared transmitter/receiver device such as a shared antenna device.
In another aspect of the present invention, a communication device uses one of the previously-described filters or the duplexer. Therefore, insertion losses into a high frequency transmitter/receiver are reduced while communication quality such as low-noise characteristics or transmission speed is improved.